Senegal President Abdoulaye Wade, who is seeking to extend his 12-year rule in the West African state despite complaints he is violating term limits, was heckled by scores of voters as he cast his ballot on Sunday.
The election comes after weeks of violent street protests against the 85-year-old's bid for a third term in office and a stream of warnings that Senegal's reputation as an established democracy now hangs in the balance.
More than a hundred people booed and chanted "Wade go away" in the local Wolof language as the visibly annoyed leader, seen as favorite against a fractured opposition, was ushered out of the polling station by his aides without giving a speech.
Foreign powers and diplomats issued last minute appeals for calm and a transparent vote, and a top African mediator failed to secure an agreement between Wade and his rivals over a shortened term for the incumbent if he won.
"We are closely watching the development of the situation. I have been concerned about what is happening there," United Nations Secretary General Ban Ki-moon told journalists when asked about Senegal during a visit to Zambia on Saturday.
Polling stations across Dakar appeared to open on time at 0800 GMT, or with only slight delays, and voting proceeded in an organised fashion, according to witnesses.
In the working class neighbourhood of Parcelles Assainies, hundreds of voters, many in their best clothes and some fingering prayer beads, lined up patiently.
"You can see the determination of the people, they want change," said Awa Faye Ndoye, a housewife, after she voted. She predicted people would take to the streets in protest if Wade was declared winner.
Despite facing heavy opposition to his candidacy among Senegal's urban youth, Wade claims strong support particularly in rural areas, and has said he is confident of a win in the election's first round of voting.